Some traditional large telescopes having a diameter of several tens of meters or larger utilize a primary mirror (a primary reflecting mirror) formed by arranging multiple segmented mirrors as described, for example, in International Publication No. 2006/006240. In order to prevent deterioration in the mirror accuracy, actuators correcting the deflected mirror surface may be utilized as described, for example, in Unexamined Japanese Patent Application Kokai Publication No. 2005-208227. Large telescopes having a diameter of several tens of meters or larger have to prevent self-weight deformation of the primary mirror. In such cases, the primary mirror is formed by segmented mirrors as mentioned above and supported at many points with a primary mirror support structure. Therefore, the mirror accuracy of the primary mirror surface (primary reflecting mirror surface) significantly relies on the rigidity of the primary mirror support structure.
In a large telescope, the orientation change due to the elevation angle change may cause self-weight deformation or distortion of the primary mirror support structure. For example, some telescope units are designed to have a significantly large height to reduce the self-weight deformation in attempting to assure a large second moment of area and reduce deformation of the primary mirror support structure.
Some telescopes employ the design concept that reduces the amount of self-weight deformation by providing semicircular rails for driving the elevation angle axis directly below the primary mirror support structure to reduce the distance between the support points.
However, in a telescope of which the primary mirror support structure has a large height, the EL axis (elevation axis) of the telescope is positioned significantly high above the AZ rail plane. Then, the telescope itself has a large height. Consequently, the number of parts is increased and the dome to house the telescope becomes larger.
Furthermore, the base receives a greater load as the size is increased, which presumably leads to scale expansion and term extension of overall construction work including foundation improvement. Then, it is required to ensure the mirror accuracy with fewer parts without increasing the height of the telescope structure. Then, in order to keep the height of the EL axis small and downsize the telescope body and dome, it is suggested that “the height of the EL axis (elevation angle axis) of the telescope is kept small” and “instead of supporting the primary mirror support structure from directly below, an EL rotation structure (semicircular rails) is provided on either side of the primary mirror support structure and the primary mirror support structure is placed in-between to support the primary mirror support structure at both sides.”
However, for example, in the case of fixing the ends of the primary mirror support structure to the ends of the EL rotation structure that are apart from each other by several tens of meters, the primary mirror surface sags significantly in the center due to self-weight deformation while virtually no deformation occurs at the ends. Consequently, the mirror accuracy is presumably deteriorated.
In order to correct the curved primary mirror surface (primary mirror), the actuators as described in Unexamined Japanese Patent Application Kokai Publication No. 2005-208227 can be utilized. However, it is not perfect because of restriction on the stroke and the like. In other words, curvature deformation itself in the primary mirror surface due to orientation change of the primary mirror support structure should be prevented.
The present invention is invented to solve the above problem and an exemplary object of the present invention is to provide a primary mirror support structure and telescope unit capable of preventing the curvature deformation itself due to orientation change of the primary mirror.